One of the races that could determine who controls the Senate next year is the surprisingly tight contest in North Dakota. Democratic Sen. Kent Conrad is retiring, and given the state's Republican leanings, it was assumed that the GOP candidate, first-term Rep. Rick Berg, would be a shoe-in to win the seat. But Democrat Heidi Heitkamp is tied with Berg, according to the most recent poll.

One reason the race is close starts with a TV ad. It shows a freight train with a long line of oil tank cars running through the North Dakota prairie — tank cars that Heitkamp says are heading out of state: "I'm Heidi Heitkamp, and in the Senate I'll fight to build another refinery in North Dakota," she says in the ad. "It'll create jobs and help lower gas prices."

It's a safe bet that few other Democrats running for the Senate this year are calling for construction of an oil refinery in their state, or charging that environmentalists are running the nation's energy policy, or are so openly critical of President Obama, as Heitkamp was at a Bismarck forum last week.

"I think the first thing that I say to the president is, 'You're wrong,' " she said at the forum. " 'You're wrong on energy. You're headed in the wrong direction. You made bad decisions. It is time for you to change your secretary of energy. It is time for you to get in the real world and give predictability.' "

Heitkamp is running in a state where an oil drilling boom has led to a 3 percent unemployment rate, the nation's lowest. It is also a place where President Obama has an approval rating of 37 percent, according to Gallup. So her advocacy of fossil fuels and criticism of the Obama administration is not just politically savvy — it's also a necessity.

At that same forum, her Republican opponent, Berg, said criticizing the Obama administration isn't enough to change energy policies. He said it will take Republican control of the Senate — which would mean a new Senate majority leader to replace Democrat Harry Reid of Nevada.

"What I want to do is switch the majority leader in the Senate from someone that says they hate coal and oil to someone that's from a coal-producing state in Kentucky," Berg says. Sen. Mitch McConnell of Kentucky is currently the top Republican in the Senate.

As hard as Heitkamp is trying to distance herself from the Obama administration and its policies, Berg's campaign is trying to hang them on her.

One ad Republicans are running says: "Let's just look at the facts. Obamacare: With over $700 billion in cuts to Medicare, Heidi is for it; Rick would repeal. Obama's higher taxes that could cost North Dakota jobs: Heidi would vote 'Yes'; Rick, 'No.' Trillions in new government spending: Heidi, for; Rick, against. You decide."

Despite North Dakota's overwhelming Republican registration advantage, just two years ago both of the state's U.S. senators and its only congressman were Democrats. But after the 2010 election, the delegation became two-thirds Republican.

University of North Dakota political science professor Mark Jendrysik says it will be tough for Heitkamp to buck the trend.

"I think it's a tall order for Heitkamp in that the built-in conservatism of the state and the recent Republican successes will make it hard to convince those people who are going to vote for [Republican presidential nominee Mitt] Romney to vote for her," Jendrysik says. "But again, I think in North Dakota, party labels count for a lot less than: Do I like this person? Have I met this person? Do they come to the church picnic? Are they at the homecoming parade?"

At this past weekend's homecoming parade at the University of North Dakota in Grand Forks, both campaigns were out tossing candy and plastic footballs along the parade route. Among the spectators was Tom Wold, a retired lawyer from Fargo and a Berg supporter.

"It's important, in my opinion, that the Republicans control the Senate," Wold says.

A little farther down the route stood Irene Melby, wearing a sticker supporting Heitkamp and watching her daughter march by in the band.

"I've liked Heidi for a long time, and I really hate negative ... stuff, and I've been a Democrat for a long time. So I almost have to, generally, go with the Democrat," Melby says.

Both sides are spending millions of dollars in advertising, a rarity in the state. Berg hopes the state's GOP registration advantage will propel him to a win, while Heitkamp hopes what she calls North Dakota's notorious ticket splitters will come through for her.

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Transcript

MELISSA BLOCK, HOST:

And finally this hour, to North Dakota, scene of an unexpectedly tight Senate race. It's one of the races that's considered key in determining which party will control the Senate.

Democrat Kent Conrad is retiring, and given North Dakota's Republican leanings, it was assumed that the GOP candidate, Congressman Rick Berg, would be a shoo-in. But according to the most recent poll, he is tied with his Democratic opponent, Heidi Heitkamp. NPR's Brian Naylor went to North Dakota to find out why.

BRIAN NAYLOR, BYLINE: One reason the race is close starts with this TV ad. It shows a freight train with a long line of oil tank cars running through the North Dakota prairie, tank cars that Heitkamp says are heading out of state.

(SOUNDBITE OF TV AD)

HEIDI HEITKAMP: I'm Heidi Heitkamp, and in the Senate, I'll fight to build another refinery in North Dakota. It'll create jobs and help lower gas prices.

NAYLOR: It's a safe bet that few other Democrats running for the Senate this year are calling for construction of an oil refinery in their state or charging that environmentalists are running the nations energy policy or are so openly critical of President Obama, as Heitkamp was at a Bismarck forum last week.

HEITKAMP: I think the first thing that I say to the president is you're wrong. You're wrong on energy. You're headed in the wrong direction. You made bad decisions. It is time for you to change your secretary of energy. It is time for you to get in the real world and give predictability.

NAYLOR: Heitkamp is running in a state where an oil drilling boom has led to a 3 percent unemployment rate, the nations lowest. It's also a place where President Obama has an approval rating of 37 percent according to Gallup. So her advocacy of fossil fuels and criticism of the Obama administration is not just politically savvy but a necessity. At that same forum, her Republican opponent, Rick Berg, said criticizing the Obama administration isn't enough to change energy policies. It will take a new Senate majority leader.

REPRESENTATIVE RICK BERG: What I want to do is switch the majority leader in the Senate from someone that says they hate coal and oil to someone that's from a coal-producing state in Kentucky.

NAYLOR: As hard as Heitkamp is trying to distance herself from the Obama administration and its policies, Rick Berg's campaign is trying to hang them on her. Here's an ad Republicans are running.

(SOUNDBITE OF AD)

UNIDENTIFIED WOMAN: Let's just look at the facts. Obamacare: With over 700 billion in cuts to Medicare, Heidi is for it; Rick would repeal. Obama's higher taxes that could cost North Dakota jobs: Heidi would vote yes; Rick, no. Trillions in new government spending: Heidi for; Rick against. You decide.

NAYLOR: Despite North Dakota's overwhelming Republican registration advantage, just two years ago, both of the state's U.S. senators and its only congressman were Democrats. But after the 2010 election, the delegation became two-thirds Republican. University of North Dakota political science professor Mark Jendrysik says it will be tough for Heitkamp to buck the trend.

MARK JENDRYSIK: I think it's a tall order for Heitkamp in that the built-in conservatism of the state, the recent Republican successes will make it hard to convince those who are going to vote for Romney to vote for her, but again, I think in North Dakota, party labels count for a lot less than do I like this person, have I met this person, do they come to the church picnic, are they at the homecoming parade.

(SOUNDBITE OF MUSIC)

NAYLOR: At this past weekend's homecoming parade at the University of North Dakota in Grand Forks, both campaigns were out tossing candy and plastic footballs along the parade route. Among the spectators was Tom Wold, a retired lawyer from Fargo and Berg supporter.

TOM WOLD: It's important in my opinion that the Republicans control the Senate. The first vote is the most important vote when they vote for either going to vote for Harry Reid or they're going for the Republican leader in the Senate, and then that's the most important vote.

NAYLOR: A little further down the route, stood Irene Melby, wearing a Heidi sticker, watching her daughter march by in the band.

IRENE MELBY: I've liked Heidi for a long time, you know? And I really hate negative type of stuff, and I've been a Democrat for a long time. So, you know, I almost have to generally go with the Democrat, so...

NAYLOR: Both sides are spending millions of dollars in advertising, a rarity in the state. Berg hopes the state's GOP registration advantage will propel him to a win, while Heitkamp hopes what she calls North Dakota's notorious ticket splitters will come through for her. Brian Naylor, NPR News. Transcript provided by NPR, Copyright NPR.